This project's long term goal is to establish the usefulness of standard Pulmonary Function Testing (PFT) in the early detection and management of Pneumocystis carinii (P. carinii) pneumonia in HIV positive patients. As the incidence of HIV positive patients increases, the need for a non-invasive and screening test for the early diagnosis of Pneumocystis carinii (P. carinii) which commonly affects such patients also increases. It is our hypothesis that PFT, which is easily performed and non-invasive, in asymptomatic HIV positive patients will allow for early detection of sub-clinical P. carinii infections. Early intervention can thus be instituted which we believe will improve treatment response rates, long term morbidity and mortality rates. Furthermore, in patients receiving anti-Pneumocystis therapy, we suspect length of therapy and therapeutic efficacy will be guided and reflected by sequential PFT. We estimate that over the next 3 years 50,000 HIV positive patients will exist in our AIDS Center's catchment area which includes 880,000 adult males and a large homosexual community. Projections from the literature suggest that at least 10,000 of these individuals will develop Acquired Deficiency Syndrome (AIDS) with 6,000 cases of P. carinii pneumonia occurring over this 3 year interval. With media coverage and "out-reach" programs we can expect to encounter a thousand or more HIV positive individuals and several hundred P. carinii pneumonias. Over a five year period we will prospectively study 720 HIV positive patients with serial PFT. Patients will be grouped based on respiratory symptoms and enter one of the following protocols: Asymptomatic patients with abnormal PFT and all symptomatic patients will undergo bronchoalveolar lavage (BAL) for definitive identification of P. carinii organisms; asymptomatic patients found to be infected with P. carinii on BAL will be randomly assigned to an aerosolized Pentamidine protocol; infected symptomatic patients will be randomly assigned to conventional parenteral therapy with or without aerosolized Pentamidine; the remaining patients, including those with negative BAL results and normal PFT, will be followed with serial PFT.